The present invention relates to a radio reception apparatus and received power amplification method.
FIG. 1 is a block diagram illustrating a configuration of a conventional radio reception apparatus employed for a communication in which a CDMA system is utilized. In a radio reception apparatus 10, a signal received by an antenna 11 is subjected to predetermined radio processing at a radio unit 12, before being outputted to an amplifier 13.
The amplifier 13 outputs a signal indicating a power value of a received signal to a controller 14. The controller 14 calculates an amplification factor from the power value of the received signal and a target power value so that the power value of signal outputted to matched filters 15, 16, and 17 from the amplifier 13 comes into constant value in conformity with the target power value. Then the controller 14 performs feedback of a control signal instructing the amplification factor to the amplifier 13. The amplifier 13 amplifies power of a received signal in accordance with the amplification factor undergoing the feedback, thus, outputting the amplified signal to the matched filters 15, 16, and 17.
Further, the power value of the received signal outputted to the controller 14 from the amplifier 13 employs an average value being average over a predetermined time interval in order to relieve an influence of a noise. Further, in the case where the radio reception apparatus 10 receives signals transmitted from a plurality of radio transmission apparatus, a power value of a received signal outputted to the controller 14 from the amplifier 13 comes into a power value of the received signal which is subjected to code division multiplexing.
The matched filters 15, 16, and 17 each gives despreading processing to an amplified signal, thus, calculating correlation value between the amplified signal and spreading code to output to demodulators 18, 19, and 20 respectively. The demodulators 18, 19, and 20 each gives predetermined demodulation processing to the amplified signals on the basis of the respective correlation values to output demodulated signals to A/D converter and so forth at latter stages.
However, there is a problem in the amplification of a received signal which is executed in the conventional radio reception apparatus as follows.
Namely, in the case where there exists users who do not transmit signals actually because the users have no data to be transmitted in an interval (hereinafter referred to as inter-communication user) in a plurality of radio transmission apparatus users who are in communication with the radio reception apparatus, the number of signals which are subjected to code division multiplexing become smaller than that in the case where the whole users transmit signals during this interval.
Consequently, in this case, an average value of the power value of the received signal outputted from the amplifier 13 to the controller 14 becomes smaller value than that in the case where the whole users transmit the signals. The controller 14 calculates an amplification factor from the average value of the smaller value and the target power value, and therefore, the amplification factor becomes lager than that in the case where the whole users transmit the signals.
Further, in the following description, a user who transmits signals actually to a radio reception apparatus while being provided with data to be transmitted in a plurality of radio transmission apparatus users, is called xe2x80x9cinter-transmission userxe2x80x9d.
Here, xe2x80x9cdata to be transmittedxe2x80x9d means voice data, image data and so forth, to be transmitted from a radio transmission apparatus, and xe2x80x9cto transmit signals actuallyxe2x80x9d means to transmit signals of voice data, image data and so forth except control signals.
In the case where the inter-communication user come into the inter-transmission user and the number of the inter-transmission users increases, since the number of signals being subjected to code division multiplexing to be outputted to the amplifier 13 from the radio unit 12 increases, the power increases. Accordingly, there is the problem that when the power of the signal is amplified in accordance with the above-described amplification factor which is calculated and then returned to the amplifier 13, the power value of the amplified signal exceeds the target power value.
In order to perform A/D conversion of the amplified signal which exceeds the target power value, since the number of bits of the A/D converter at a latter stage of the demodulators 18, 19, and 20 is required to be increased with surplus beforehand, thus the transmission efficiency deteriorates.
It is an object of the present invention to provide a radio reception apparatus and received power amplification method capable of calculating an appropriate amplification factor so that a power value of a received signal which is amplified does not exceed a target power value even when the number of inter-transmission users is changed.
The present inventor notes that the power value of the amplified signal exceeding the target power value is caused by the matter that an amplification factor is calculated on the basis of only the power value of the received signal. Thus the inventor finds that it is possible to calculate an appropriate amplification factor by considering the number of the inter-transmission users and the number of the inter-communication users, to achieve the present invention.
Accordingly, in the present invention, in order to achieve the above-mentioned object, the radio reception apparatus calculates a power value of a received signal per one person of inter-transmission users from both of a power value of the received signal and the number of the inter-transmission users, thus estimating a power value in the case where the whole inter-communication users come into inter-transmission users.